First stab at some statsd reporting
Allow bucket to be provided to statsd.StatClient.

Prefixes the bucket name to the application part of the stat key.
Add bucket name to statsd stats.
Prefix 'unknown' to stat if no bucket is provided.
Merge branch 'master' into add-statsd

Conflicts:
	backdrop/write/api.py
PEP8
PEP8

One new line character at the end of the file but *not* another one because that would be a crime!